The objectives of this study are to evaluate safety and tolerability of multiple oral doses of DMP 777 in three different dose levels; to determine pharmacokinetic and pharmacodynamic characteristics of multiple oral doses of DMP 777 at three different dose levels; and to define DMP 777 dosage level necessary to achieve sustained high-level systemic neutrophil elastase inhibition as determined by measurements of circulating PMN-lysate AAPVase inhibition and whole blood urea fragment levels in a selectively defined cohort of patients with cystic fibrosis following twice daily (every twelve hours) oral administration of DMP 777 for nine days duration. This is a multicenter, randomized, double-blind, placebo-controlled, dose-escalation design. Patients will be entered in one of three DMP 777 dosing groups across three sequential cohorts. Patients will be required to remain confined in a clinical research unit or similar facility for two periods, each a minimum of 24 hours, on Day 1 and Day 7.